Describe the pull-based outbound oracle pattern: its problem, solution, and main trade-off.

The outside world needs data that lives on the chain, so it queries an oracle that reads and filters the chain and returns the answer. Initiated off-chain; fastest of the four because it just reads existing state.

• Problem: Knowledge stored on the chain is needed outside it, but the closed chain can't be directly queried by the outside world.
• Solution: The oracle lets off-chain components call in to query and filter blockchain data, returning the relevant slice.
• Benefit: It decouples external requests from the actual on-chain retrieval, giving the outside world a uniform way to access and query chain data on demand.
• Drawback: Depending on the chain's size and how well the location of the wanted data is known, gathering the answer can take some time. Because it only reads existing state (no transaction to mine), it is in practice the fastest pattern — sub-second in measurements (~0.13 s mean).

Go deeper:

• Foundational Oracle Patterns (Mühlberger et al., arXiv) — the pull-based outbound pattern and the measurements showing why reading existing state makes it fastest.